1. Field of the Invention
The present invention relates to conduit systems and more particularly relates to conduit systems in which adjacent ends of conduit units of the systems are sealingly coupled in the field during installation.
2. The Prior Art
The prior art has proposed conduit systems in which individual conduit units of a system carry an integral coupling arrangement for sealingly coupling adjacent ends of two conduit units together. Although such coupling units have enabled thermal expansion and contraction of pipes in the conduit units while maintaining a sealed relationship between the pipes, the construction of conduit units with integral couplings complicated the process by which the conduit units were constructed thus increasing the cost of the conduit units. Furthermore, assembly of these conduit units in the field was sometimes difficult, time-consuming, and at times lead to damages to the seals between them. U.S. Pat. No. 3,492,029 to French, et al., issued Jan. 27, 1970 is illustrative of such systems.
In order to simplify the construction and installation of conduit systems as well as to better accommodate thermal expansion and contraction of the conduit pipes the prior art proposed conduit systems having conduit units interconnected by individual coupling units. The coupling units enabled the conduit units to be more simply constructed and provided space for thermal expansion and contraction of the conduit pipes. U.S. Pat. No. 3,854,756 to Couch, issued Dec. 17, 1974 disclosed such a conduit system construction.
Many prior art conduit systems were susceptible to infiltration of moisture into the insulation around the pipes as well as into contact with the pipes themselves as a result of thermal expansion and contraction of the pipe breaking seals at the ends of the conduit units. Conduit systems of the character referred to are sometimes buried in the ground which gives rise to the possibility of ground water infiltration into the juncture of conduit units with each other or with coupling units. When the conduit systems are installed above ground, moisture from the elements as well as moisture resulting from atmospheric water vapor can infiltrate the systems. Even in conduit systems employing coupling units constructed to minimize the effects of temperature responsive expansion and contraction of the conduit pipes, moisture infiltration tended to occur along sealing faces at the junctures of the conduit and coupling units.
In conduit systems employing ferrous pipes, infiltration of moisture at the joints between the couplings and the conduit units tended to cause serious corrosion problems. In addition to corrosion tending to cause the pipe itself to fail, pipe corrosion was apt to cause destruction of seals between the couplings and adjacent pipe ends due to abrasion of the coupling seals as corroded pipes changed length and shifted relative to the seals due to temperature variations.